Question

How many moles of water are there in 1.500 L at STP? How many molecules?

Answer 1

Sol. :- At STP, the density of water is 1g/ml. So we have 1500 gram of water.

Molar mass of water = 2$\times$mass of hydrogen + Mass of oxygen (As water is H₂O)

Molar mass of water = 18.003 g/mole

So, No. of moles in 1.5 L of water at STP = 1500/18.003 moles

which is approximately 83.3 moles of water.

Now we know that

1 mole of water = 6.022 $\ast10$²³ molecules of water

So No. of molecules in 1.5 L of water = $83.3\times 6.022\times 10^2^3$ molecules of water

which is around  $5.016\times 10^2^5$ molecules of water.